1. Field of the Invention
The present invention relates generally to an output control system for an internal combustion engine for an automotive vehicle. More specifically, the invention relates to an engine output control system for adjusting an engine output depending upon a selected speed ratio of a power transmission.
2. Description of the Background Art
In automotive vehicles, power transmissions are provided for selecting appropriate speed ratios depending upon vehicle driving conditions. The power transmission thus variable of its output depending upon the engine output and the selected speed ratio. At various speed ratio of the power transmission, it is desirable to provide different engine output characteristics so as to adapt to the selected speed ratio.
For example, Japanese Patent First (unexamined) Publication (Tokkai) Showa 57-93681 discloses a control system for an internal combustion engine, which control system controls output characteristics of the engine. In the disclosed system, spark advance angle is adjusted depending upon the speed ratio of the power transmission. For instance, the control system is responsive to shifting up on the speed ratio for temporarily retarding spark advance angle for lowering engine output torque for smooth transition during transmission gear shifting up. Temporary retarding of spark advance angle may assist for prevention of engine knocking and thus prevents the spark advance angle from being excessively retarded.
On the other hand, in the modern automotive technologies, engine output performance is significantly improved to provide higher engine power. Higher performance of the engine may cause difficulty in adjusting the driving power provided by the engine at certain driving conditions. Particularly, when it is required to drive the vehicle at very low speed, such as a speed lower than human walking speed, difficulty is encountered in adjusting the vehicle speed by adjusting the engine driving power. For example, in backward driving, in the transmission reverse gear position, a low vehicle driving speed is preferred. Due to high engine performance, delicate accelerator control becomes necessary for adjusting the vehicular speed at substantially low speed.